Gear box with two pinion shafts

ABSTRACT

A variable-speed gearbox comprises a main transmission ( 2 ) arranged in a housing ( 30 ) and a downstream range-change transmission ( 32 ), the range-change transmission having power distribution on two countershafts ( 12, 14 ). On a main shaft ( 4 ) of the main transmission ( 2 ), a gear wheel ( 6 ) is arranged in a radially movable manner which meshes with respective first gear wheels ( 8, 10 ) each on one of the countershafts. In the housing of the variable-speed gearbox, a drive output shaft ( 22 ) is radially and axially fixed which is connected a gear wheel ( 20 ) that meshes in each case with a second gear wheel ( 16, 18 ), respectively, on each of the countershafts. The gear wheel on the main shaft that meshes with the first gear wheels on the countershafts is maintained in its axial position relative to the drive output shaft by way of pressure combs ( 50, 52, 54, 56 ).

This application is a national stage completion of PCT/EP2004/009876filed Sep. 4, 2004 which claims priority from German Application SerialNo. 103 46 658.4 filed Oct. 8, 2003.

FIELD OF THE INVENTION

The invention concerns a gearbox with two countershafts for powerdistribution.

BACKGROUND OF THE INVENTION

Modern, powerful vehicle gearboxes usually comprise a main transmissiongroup with a multi-stage basic gear and an upstream or downstreamsplitter group and/or a downstream range gear group. In a gearboxhousing, they mainly comprise an input shaft as a first shaft and acentral or main shaft as a second shaft, which can also be the outputshaft, as well as one or more countershafts. The input and main shaftsare essentially concentric with one another.

Having regard to the running properties and smooth running, suchgearboxes can be designed with helical gearing, at least for the forwarddriving range. The axial forces from the helical gearing have to betaken up by an axial bearing and transmitted to the housing.

Gearboxes with the structure described can have one or morecountershafts.

In gearboxes with power distribution between two countershafts, the maintransmission group comprises two shafts arranged essentially one behindthe other, one of which, namely either the input shaft or the main shaftof the main transmission, is mounted radially and axially fixed, whilethe respective other shaft is mounted floating laterally, i.e., able tomove radially to allow the necessary load equalization. In this, careshould be taken that an easy swivelling motion of the floating shaft ispossible.

In gearboxes with two countershafts, the load equalization canpreferably be designed such that the input shaft is mounted fixed on thehousing, the countershafts are fixed on the housing and the main shaftis mounted floating in the gear wheels involved in the force flow.

The known variable-speed gearboxes for goods vehicles have a three- orfour-speed main or basic transmission section and an upstream ordownstream splitter transmission as an auxiliary transmission, whichdoubles the number of gear speeds of the main transmission since itsplits the transmission ratio steps of the main transmission. Arange-change transmission downstream from the main transmission extendsthe ratio range of the main transmission. The range-change transmissioncan be in the form of a planetary gearset or in the form of anarrangement of spur gear wheels.

From EP-A1 0 009 775 a range-change transmission with spur gear wheelsdownstream from a main transmission with two countershafts for powerdistribution is known. The range-change transmission has twocountershafts which are rotationally independent of the countershafts ofthe main transmission. A floating gear wheel is arranged on the mainshaft of the gearbox, which meshes with a gear wheel on each of thecountershafts of the range-change transmission. This gearbox does nothave sufficient capacity for absorbing axial forces that result from thegearing.

From DE-A1 196 04 824 by the present Applicant, a variable-speed gearboxwith a range-change transmission of planetary design has become known.On the gearing of the planetary transmission pressure combs are providedto take up the axial forces that result from the helical gearing. Thecontent of DE-A1 196 04 824 is intended to be fully incorporated in thepresent application.

The purpose of the present invention is to improve the axial mounting ina gearbox with two countershafts for power distribution.

SUMMARY OF THE INVENTION

In a range-change transmission with spur gears, the gear wheel arrangedon the main shaft, which meshes with gear wheels on the countershafts ofthe range-change transmission, reaches very high rotation speeds in thedisengaged condition in the fast shift position of the range-changetransmission. This makes mounting with axial bearings problematic.Accordingly, the invention proposes a variable-speed gearbox with a maintransmission arranged in a housing and a downstream range-changetransmission, in which the range-change transmission comprises powerdistribution to two countershafts and in which a gear wheel is arrangedin a radially displaceable manner on a main shaft of the maintransmission. This gear wheel meshing in each case with a first gearwheel on each respective countershaft and in which a drive output shaftis arranged radially and axially fixed in the housing of thevariable-speed gearbox; to that shaft is connected a gear wheel whichmeshes in each case with a second gear wheel on each respectivecountershaft. Pressure combs are provided by way of a gear wheel on themain shaft which meshes with the first gear wheels of the countershaftis maintained in its axial position relative to the drive output shaft.More preferably, the countershafts are maintained in their axialposition relative to the drive output shaft by way of pressure combs.

In a particularly advantageous embodiment of the invention, thegearwheel on the drive output shaft comprises pressure combs which arein contact with pressure combs formed on the second gear wheels of thecountershafts in order to take up axial forces. The gear wheel on themain shaft has pressure combs which are in contact with pressure combsformed on the first gear wheels of the countershafts in order to take upaxial forces.

Particularly advantageous is the drive output shaft, held radially andaxially in the housing by a double conical-roller bearing arrangement.

In another advantageous embodiment, the countershafts have only oneradial mounting in the housing, Which preferably comprises rollerbearings.

The countershafts and the gear wheel on the main shaft are guided andmaintained axially with the help of the pressure combs. The lubricationof the pressure combs can take place from outside and is simple andeffective. During the torque transmission by the gear wheels of thecountershafts, no axial gear forces have to be taken up by the bearingsand transferred to the housing. Thus, the axial mounting of thecountershafts can be omitted and the countershafts need only be held inradial-mounting roller bearings. The entire gearset combination of therange-change transmission is fixed axially by the mounting of the driveoutput shaft.

Exact formation of the pressure combs on the gear wheel of the mainshaft ensures that while the axial fixing is maintained, the necessaryradial freedom of the movement is secured.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described, by way of example, with referenceto the accompanying drawing in which:

FIG. 1 is a diagrammatic gearbox with two pinion shafts.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, in a variable-speed gearbox (not illustrated in greaterdetail), a main transmission 2 comprises a main shaft 4, at the end ofwhich is arranged a gear wheel 6 with some radial play. For this, theradial mounting of the gear wheel 6 is provided with its outer teethengaging only in the outer teeth of two first gear wheels 8 and 10. Ineach case, the first gear wheels 8 and 10 are fixedly arranged onrespective countershafts 12 and 14 or formed as one piece with thecountershafts. Each countershaft 12, 14 has a respective secondgearwheel 16 and 18, in each case again fixed on its countershaft 12 and14 or made as one piece with the countershafts 12, 14.

With their outer teeth, the two second gear wheels 16 and 18 mesh withthe outer teeth on a gear wheel 20 arranged fixed on a drive outputshaft 22 of the variable-speed gearbox or made as one piece therewith.To the drive output shaft 22 is attached a drive output flange 24 bywhich the variable-speed gearbox is connected to further elements of avehicle drive train (not illustrated here).

The drive output shaft 22 is mounted by two conical-roller bearings 26and 28 in a housing 30 of the variable-speed gearbox or of arange-change transmission 32 downstream from the main transmission 2.Also mounted in the housing 30 are the two countershafts 12 and 14, eachin two roller bearings 34, 36 and 38, 40 respectively. These rollerbearings 34, 36, 38, 40 only take up radial forces and transfer them tothe housing 30. All the gear teeth of the gear wheels 8, 10, 16, 18, 20are of the helical-tooth type from which axial forces result for theabsorption and transfer of which the roller bearings 34, 36, 38, 40 arenot suitable.

A gearshift sleeve 42 is arranged at the end of the main shaft 4 iswhich, by virtue of inner teeth, is connected with the main shaft 4rotationally fixed but able to be displaced axially. By way of a controlmechanism (not shown here), the gearshift sleeve 42 can be movedaxially. When this happens, the gearshift sleeve 42 with its outer teeth48 connects the main shaft 4 either with inner teeth 44 on the gearwheel 6 on the main shaft 4 or with inner teeth 46 of the drive outputshaft 22 to form a direct connection between the main shaft 4 and thedrive output shaft 22. If desired, the gearshift sleeve 42 can alsoadopt a neutral shift position in which there is no connection witheither of the inner teeth sets 44, 46.

The drive output shaft 22 is mounted axially fixed in the housing 30 bymeans of the conical-roller bearings 26 and 28. Laterally on the outerteeth of the gear wheel 20 on the drive output shaft 22 respectivepressure combs 50 and 52 are arranged. The pressure surfaces on thepressure combs 50 and 52 react with correspondingly formed pressuresurfaces on the gear wheels 16 and 18, thereby fixing the countershafts12 and 14 in the axial direction. Thereby, the gear wheels 8 and 10 onthe countershafts 12 and 14 are also fixed axially.

Laterally on the outer teeth of the gear wheel 6 on the main shaft 4,respective pressure combs 54 and 56 are arranged. The pressure surfaceson the pressure combs 54 and 56 react with correspondingly formedpressure surfaces on the gear wheels 8 and 10 on the countershafts 12and 14. Since the gear wheels 8 and 10 are axially fixed, as describedabove, the gear wheel 6 is also axially fixed by virtue of the pressurecombs 54 and 56 so that the problems associated with axial mounting athigh rotation speeds of the gear wheel 6 are eliminated.

REFERENCE NUMERALS

-   2 main transmission-   4 main shaft-   6 gear wheel-   8 gear wheel-   10 gear wheel-   12 countershaft-   14 countershaft-   16 gear wheel-   18 gear wheel-   20 gear wheel-   22 drive output shaft-   24 drive output flange-   26 conical-roller bearing-   28 conical-roller bearing-   30 housing-   32 range-change transmission-   34 roller bearing-   36 roller bearing-   38 roller bearing-   40 roller bearing-   42 gearshift sleeve-   44 inner teeth-   46 inner teeth-   48 outer teeth-   50 pressure comb-   52 pressure comb-   54 pressure comb-   56 pressure comb

1-6. (canceled)
 7. A variable-speed gearbox with a main transmission (2)arranged in a housing (30) and a downstream range-change transmission(32), the range-change transmission (32) having power distribution ontwo countershafts (12, 14), a gear wheel (6) being arranged radiallymovably on a main shaft (4) of the main transmission (2), which meshesin each case with a first gear wheel (8, 10) respectively on one of thecountershafts (12, 14), and in the housing (30) is arranged a radiallyand axially fixed drive output shaft (22) with which is connected a gearwheel (20) that meshes in each case with a second gear wheel (16, 18)respectively on the two countershafts (12, 14), the gear wheel (6) whichmeshes with the first gear wheels (8, 10) of the countershafts (12, 14)is maintained on the main shaft (4) in an axial position relative to thedrive output shaft (22) by pressure combs (50, 52, 54, 56).
 8. Thevariable-speed gearbox according to claim 7, wherein the twocountershafts (12, 14) are maintained in the axial position relative tothe drive output shaft (22) by first and second pressure combs (50, 52).9. The variable-speed gearbox according to claim 7, wherein the gearwheel (20) on the drive output shaft (22) has first and second pressurecombs (50, 52) which contact with pressure combs formed on the secondgear wheels (16, 18) of the countershafts (12, 14) in order to take upaxial forces, and the gear wheel (6) on the main shaft (4) has third andfourth pressure combs (54, 56) which contact with pressure combs formedon the first gear wheels (8, 10) of the countershafts (12, 14) in orderto take up axial forces.
 10. The variable-speed gearbox according toclaim 7, wherein the drive output shaft (22) is held radially andaxially in the housing (30) by double conical-roller bearings (26, 28).11. The variable-speed gearbox according to claim 7, wherein thecountershafts (12, 14) only has a radial mounting (34, 36, 38, 40) inthe housing (30).
 12. The variable-speed gearbox according to claim 11,wherein the radial mounting comprises roller bearings (34, 36, 38, 40).13. A variable-speed gearbox and a main transmission (2) arranged in ahousing (30) with a downstream range-change transmission (32), thevariable-speed gearbox comprising: at least one countershaft (12, 14)for the power distribution; a main shaft (4) of the main transmission(2) having a main gear wheel (6) which is radially movable about themain shaft (4), the main gear wheel (6) engages a first gear wheel (8)of a first countershaft (12) and a second gear wheel (10) of a secondcountershaft (14); an axially fixed drive output shaft (22) is rotatablysupported in the housing (30) and has a fixed gear wheel (20) thatengages both a third gear wheel (16) of the first countershaft (12) anda fourth gear wheel (18) of the second countershaft (14); and aplurality of pressure combs (50, 52, 54, 56) axially supported the maingear wheel (6) on the main shaft (4) in an axial position relative tothe drive output shaft (22).